Living organisms conduct complicated motor control, and then it is very significant to clarify the control mechanism in a field of ergonomics or the like. A lot of approaches to measure and analyze the nerve-muscle action have been tried in order to elucidate the control mechanism in vivo.
Muscles consist of multiple sub-units referred to as motor units. The motor unit consists of a single α motor neuron (hereinafter referred to as α-MN) in a spinal cord and a muscle fiber group dominated by the α-MN, and is a minimum function unit of a nerve-muscle control mechanism. When the muscle contracts, the multiple motor units act in a cooperative manner. In order to elucidate the nerve-muscle control mechanism it is important to measure a motor unit action potential (hereinafter referred to as an MUAP) and to analyze each action style.
An electromyogram showing a change of an electric potential generating in accordance with contraction of muscle is measured as an interference waveform of multiple MUAPs. There are a needle electromyogram measured by the use of needle electrodes stinging in muscles and a surface electromyogram measured by the use of non-invasive surface electrodes as the electromyogram.
Since the needle electromyogram has merits such that it is not susceptible to living organism tissue and it can separate the motor unit relatively easily, the needle electromyogram is used for analyzing the electromyogram by separating it into the motor units. (K. C. McGill, K. L. Cummins, and L. J. Dorfman, “Automatic Decomposition of Clinical Electromyogram”, IEEE Trans. Biomed. Eng. BME, vol. 32, pp. 470-477, 1985) Since the surface electromyogram can be measured by attaching surface electrodes to a surface of skin, it has a merit that the surface electromyogram can be measured relatively easily compared with the needle electromyogram.
However, since it is necessary for the needle electromyogram to sting needle electrodes on muscles in order to measure the electromyogram and there is a problem that load is applied to living organisms, it has been difficult to measure multiple muscles at a time. In addition, a portion where the needle electrodes measure is a very narrow range, and which portion is to be measured in a tissue of a living organism has to be settled previously. Meanwhile, since the surface electromyogram monitors multiple MUAPs locating under the electrodes in a spatially and temporally added state, it is difficult to extract a firing pattern of an individual motor unit.